The invention relates to a method and to a control unit for permitting reliable detection of a blocked electric machine in an electric vehicle.
In electric vehicles or hybrid vehicles, an electric machine which can usually be operated either in a drive mode or in a generator mode is generally connected to one or more wheels of the vehicle. The electric machine in this context can be connected directly and rigidly to the wheel or the wheels since, in contrast to internal combustion engines, it can be stopped completely and set in rotation against at any time. However, in particular in the case of hybrid vehicles in which, in addition to the electric machine, an internal combustion engine for driving the vehicle is also provided, it can be advantageous not to connect the electric machine directly to the wheel or the wheels but instead via a clutch. In this way, in particular in a driving state in which the vehicle is to be driven only by the internal combustion engine, the electric machine can be decoupled from the rotating wheels and in this way power losses as a result of the electric machine being entrained are avoided.
Synchronous machines, such as are used typically nowadays in electric vehicles or hybrid vehicles, have a rotor which can rotate within a stator. In this context, the rotor is separated from the stator only by a small gap. It has been observed that, for example in the cases of extreme stress or severe wear, the rotor can become blocked within the stator. Since such blockage can lead to blockage of the wheels coupled to the electric machine and therefore to dangerous driving situations and to more wide-ranging damage to the electric machine or to the entire vehicle, the electric machine should be reliably and continuously be monitored for the occurrence of blockage.